High-voltage inductive coil

ABSTRACT

A high-voltage output coil for use in an ignition system transformer. The frequency of the input energy is on the order of 10,000 Hertz and is square-wave in form. The coil has a wide strip first turn for preventing insulation burn-out caused by radio-frequency current flow.

United States Patent 1 1 Canup et al.

[4 1 May 27, 1975 HIGH-VOLTAGE INDUCTIVE COIL [75] inventors: Robert E.Canup, Chester; Earl W.

McPeak, Jr., Powhatan, both of Vav [73] Assignee: Texaco Inc., New York,NY.

[22] Filed: Aug. 22, 1973 [2]] Appl. No.1 390,474

[52] US. Cl. 336/70; 336/84; 336/223 [5|] Int. Cl. 1101f 27/28 [58]Field of Search 336/70, 69, 84, 206, 223

[56] References Cited UNITED STATES PATENTS Erikson 336/84 PrimaryExaminer-Th0mas J. Kozma Attorney, Agenl, or FirmT. H. Whaley; C. G.Ries; Henry C. Dearborn [57] ABSTRACT A high-voltage output coil for usein an ignition system transformer. The frequency of the input energy ison the order of l0,000 Hertz and is square-wave in form. The coil has awide strip first turn for preventing insulation burn-out caused byradio-frequency current flow.

12 Claims, 3 Drawing Figures HIGH-VOLTAGE INDUCTIVE COIL BACKGROUND OFTHE INVENTION l. Field of the Invention This invention concernsinductive coil structure, in general. More specifically, it relates toan improvement for a high-voltage secondary winding of a transformer,e.g., a high-frequency, high-voltage transformer adapted to be used inignition systems.

2. Description of the Prior Art Heretofore, in the construction of ahigh-voltage, relatively low-current transformer of the type that wasemployed in an ignition system, there has been a diff"- culty thatdeveloped which resulted in burning out insulation. It causedshort-circuiting of some inner turns of the transformer and consequentbreakdown in its operation. It was particularly found to be true inignition systems where the transformer is employed with asquare-wave-type oscillator to develop a highfrequency spark outputvoltage.

The known type of winding structure employed an insulating sleevedesigned to fit over a magnetic core and upon which a large number ofturns would be wound. Thus, a large plurality of winding layers would bebuilt up around the insulating sleeve, and the ends of such windingwould be brought out for connection to an electrical output circuit. Itwas discovered that with such structure, when high-frequency square-wavesignals were induced in the winding, there was a substantial build-up ofradio-frequency energies that would cause breakdown or burn-out of theinsulation between winding turns and layers of the windings.

It is an object of this invention to provide a first single turn ofwinding conductor that is made up of a wide conductive-material stripwhich extends over the entire width of the winding. It is a genuinefirst turn of the winding so that, thereafter, the multiple turns andplurality of layers of such turns are wound thereover.

SUMMARY OF THE INVENTION Briefly, this invention concerns a high-voltageinductive coil. It comprises in combination a large plurality ofwindings including multiturn layers of an electrical conductor fordeveloping a high-voltage output. The first turn of said windingscomprises a unitary strip extending substantially over the entire widthof said multiturn layers.

Again, briefly, the invention pertains to a transformer for use with anignition system that employs a squarewave oscillator operating at afrequency on the order of 10,000 Hertz. The transformer employs ahighvoltage output winding having means for avoiding insulationburn-out, which means and winding comprise a core tube for supportingsaid winding thereon, and the tube is adapted to receive a magnetic coretherethrough. It also comprises a conductive-material strip having abeginning and an ending, and being at least as wide as said winding. Thesaid strip is wound around said core tube with said ending overlappingsaid beginning. The output winding also comprises electrical in sulationmeans for separating said overlapping portions of said strip. The saidwinding is wound over said strip with the inner end electricallyconnected to said strip ending so that said strip forms the first turnof said winding. The winding also comprises means for making anelectrical circuit connection to the beginning of said strip.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects andbenefits of the invention will be more fully set forth below inconnection with the best mode contemplated by the inventors of carryingout the invention, and in connection with which there are illustrationsprovided in the drawings, wherein:

FIG. I is a schematic cross-sectional view illustrating the prior art;and

FIG. 2 is a schematic cross-sectional view illustratingtransformer-winding structure according to the invention, and

FIG. 3 is a transverse cross-sectional view taken along the lines 3-3 ofFIG. 2, looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT In connection with ignitionsystems which employ high-frequency continuous-wave spark energy, andparticularly where the energy is square-wave in form, difficulties havebeen encountered in the structure relating to the output winding of thetransformer which delivers the spark signals to the distributor. Thebasic operating frequency, under load, of such ignition systems is onthe order of 10,000 Hertz, and because the output wave form isessentially a square-wave, there are harmonics present which reachseveral megahertz.

It is to be understood that the term Hertz" has been accepted as meaningcycles per second in connection with electromagnetic waves of all sorts.Consequently, the term megahertz, of course, means millions of cyclesper second. Such meanings will be attributed throughout this applicationunless a contrary meaning is clearly expressed.

In ignition systems for use with internal combustion engines, theforegoing radio-frequency harmonics have been found to be present on thewhole engine and associated equipment. The ground return for suchradiofrequency energy is through the frame of the total ignition systemequipment and to the ground strap of the transformer which has theforegoing output winding thereon. However, it was found that themagnitude of the radio-frequency energies was sufficient that sparkscould be drawn quite widely over the whole engine assembly. Furthermore,it was found that this radiofrequency energy included a path such thatthere would be current flow by capacitive action from the corelaminations of the transformer to the winding layers of the transformerbeginning with the first. Of course, the potential gradient wouldincrease as the electrical distance from the ground potential becamegreater, and experience indicated that current flow was great enoughnear the far end of the first winding layer to destroy the insulation onthe wires and cause shortcircuited turns. Such short-circuited turnscaused the ignition system to become inoperative.

Although it was found that the location where the foregoing burn-out ofinsulation occurred was only about 200-250 turns above ground out of atotal number of 9,000 or so on the output winding of the transformer,and the potential of the fundamental frequency at that location was lessthan 1,000 volts peak above ground, it was discovered that theradio-frequency potentials reached much greater amplitudes than that, as

' indicated by the burn-outs. However, by employing this invention whichpertains to the first turn of the winding, burn-outs may be prevented.

In order to fully understand the invention, reference may first be hadto FIG. 1 which illustrates prior art. Thus, heretofore, a transformeroutput winding of the type applicable to this invention, was wound overa magnetic core 11. However, the winding was first accomplished bywinding on the outside of an insulatingmaterial sleeve 12 that isadapted to fit over the core 11. A plurality of layers of winding turns15 would be wound over the sleeve 12 in a conventional manner.

It will be understood that the drawing is schematic and not to scale.Also, the spacing between individual turns 15 of the winding layers isgreatly exaggerated, and actually individual winding turns 15 would beinsulated from one another by having a conventional coating (not shown)on the wire filaments. However, individual layers of windings 15 areinsulated from one another by layers of insulation 16, as illustrated.It will be understood that the free end of the first turn of wind ings Iis brought out for making an electrical connection. Of course, this maybe done in any feasible manner, e.g., as indicated. by a wire 19 whichis shown connected to electrical ground by having good metal'tometalcontact with the core 11 at a point 20 indicated.

As indicated previously, the prior art structure was subject to abuild-up of radio-frequency energies between the winding turns and theground potential of the core 11 so that radio-frequency currents wouldflow through the insulating sleeve 12, as indicated by the arrows 22 inFIG. 1. It was found that these currents soon became destructive andcaused burn-out of the transformer.

FIG. 2 illustrates a transformer coil structure according to thisinvention and in a similarly schematic manner as the showing of FIG. 1.Thus, the spacing between individual turns of the winding is greatlyexaggerated, and the drawing is generally not to scale.

In FIG. 2, it will be observed that the transformer structureillustrated includes a magnetic core 25 that may be a conventionallaminated magnetic material. Surrounding the core 25, there is aninsulating-material sleeve 26. It takes the form of a so-called coretube which is adapted for being fitted closely over the core 25. Suchtube 26 may be constructed of any appropriate insulating material, e.g.,a good insulating grade of fiber or paper board. Surrounding sleeve 26,there is a conductive-material strip 29 that is made of any goodconductor, e.g., copper. It has a width sufficient to extendsubstantially the entire width of a coil 28 that is wound thereover.

Strip 29 forms the first complete turn of the transformer winding 28,and it has a beginning and an ending with sufficient length to completeat least a full turn around the sleeve 26 with some overlap. However,there is insulation provided between the overlapping ends so that thestrip 29 is not merely a continuous shield, but acts as the first turnof the winding.

Connected to the beginning of strip 29, by any feasible means, there isa conductor 30. It is carried out through the sleeve or core-tubestructure for making electrical connection to the inner end of the coil.Thus, as illustrated in FIG. 2, the conductor 30 is grounded by havinggood electrical connection to core 25. This is schematically indicatedby a contact point 31 at the end of the conductor 30. It will beappreciated that other arrangements for making desired electricalconnection to the beginning end of the strip 29 might be used. Suchother arrangements include the bringing of a narrow portion (not shown)of the strip through the insulating sleeve 26 so as to make goodelectrical contact with the surface of the core 25. This would meancutting a slit (not shown) in the sleeve 26 to permit the narrow portion(not shown) of the strip to extend through, and make intimate contactwith the core 25 on the inside ofthe sleeve or core tube 26. However,such an arrangement would be quite clear to anyone skilled in the art,and no specific illustration thereof has been made.

After the strip 29 has been wound around the sleeve 26 for a completeturn, it is continued far enough to have some overlap (not ilustrated).Also, some insulation is provided at the area of overlap. This creates afirst turn of the transformer winding without any shortcircuitingthereof.

Connected to the outside overlapping end of strip 29 is an end of anelectrically conductive-material fila ment which is employed in windingadditional turns, e.g., windings 34, as illustrated. Successive windinglayers of the filaments 34 are separated by insulatingmaterial layers35. This insulation is conventional in form and substance. It may bemade of an appropriate type of electrically insulating paper having thefull width of the winding structure.

It may be noted that a transformer according to this invention, which isparticularly for use in an ignition system, will be constructed with atotal number of turns on the order of 9,000.

In addition to employing the wide first-turn radiofrequencycurrent-shunting effect, described above, a transformer according tothis invention may also make use of a similar last complete turn. Forexample, in FIG. 2, there is a conductive strip 40 that has its innerend connected to the last of the filament turns 34. There is aninsulating layer, e.g., layer 41 that separates the overlap of strip 40as it goes around far enough to make the full outer turn of thewindings. At the outer, or free end of strip 40, there is an electricalconductor 42 which is brought out in a conventional manner for makingthe electrical connection to the output circuit of the transformer. Useof a wide outer turn to obtain anticorona effects has been employed inthe subject type of transformer Construction as shown in US. Pat. No.3,394,331 which is assigned to the same assignee as this invention.However, there was no concept relevant to a total transformer structureaccording to this invention.

While the invention has been described above in considerable detail andin accordance with the applicable statutes, this is not in any way to betaken as limiting the invention but merely as being descriptive thereof.

We claim:

l. High-voltage AC inductive coil, comprising in combination a largeplurality of winding turns beginning at the inside of said coil andincluding multi-turn layers of an electrical conductor for developing ahighvoltage output,

the first turn of said winding turns comprising a unitary strip having abeginning and an ending and extending laterally substantially the entirewidth of said multiturn layers, said ending overlapping said beginningand being insulated at said area of overlap, and

means for connecting a lead conductor to said beginning of the firstturn. 2. An inductive coil according to claim 1, further comprisingfirst electrically insulating sleeve means for supporting said windingsand being adapted to receive a magnetic core therein. 3. An inductivecoil according to claim 2, further comprising second insulating meanslocated between each of said layers, and third insulating means forseparating each turn of said conductor from the others. 4. An inductivecoil according to claim 3, further comprising electrically conductivemeans for connecting said lead conductor of said first turn to ground.5. An inductive coil according to claim 4, wherein said conductive meansis connected to said magnetic core. 6. An inductive coil according toclaim 3, further comprising at least a last turn of said winding turnscomprising a unitary strip having a beginning and an ending andextending laterally substantially the entire width of said multiturnlayers, said ending overlapping said beginning and being insulated atsaid area of overlap, and means for connecting a lead conductor to theoutside end of said coil. 7. An inductive coil according to claim 4,further comprising at least a last turn of said winding turns comprisinga unitary strip having a beginning and ending and extending laterallysubstantially the entire width of said multiturn layers, said endingoverlapping said beginning and being insulated at said area of overlap,and means for connecting a lead conductor to the outside end of saidcoil. 8. An inductive coil according to claim 5, further comprising atleast a last turn of said winding turns comprising a unitary striphaving a beginning and and ending and extending laterally substantiallythe entire width of said multiturn layers, said ending overlapping saidbeginning and being insulated at said area of overlap, and means forconnecting a lead to the outside end of said coil. 9. High-voltage ACinductive coil adapted for use in a secondary winding of a transformerfor use in an ignition system including a continuous square-wave-typeoscillator, comprising in combination a large plurality of winding turnsbeginning at the inside of said coil and including multiturn layers ofan electrical conductor for developing a high-voltage output, at leastthe first complete turn of said winding turns comprising a unitary striphaving a beginning and an ending and extending laterally substantiallythe entire width of said multiturn layers, said ending overlapping saidbeginning and being insulated at said area of overlap,

means for connecting a lead conductor to said beginning of the firstturn,

an electrically insulating sleeve for having said windings wound thereonand adapted to receive a magnetic core therein,

an insulating-material layer located between each of said windinglayers,

insulating means for separating each of said turns from the others,

at least a last complete turn of said winding turns comprising a unitarystrip having a beginning and an ending and extending laterallysubstantially the entire width of said multiturn layers and said endingoverlapping said beginning and being insulated at said area of overlap,and

means for connecting a lead to the outside end of said coil,

an electrically conductive lead connector for making an electricalconnection between said beginning of said first turn and ground,

said ground including said magnetic core.

10. In a transformer for use with an ignition system, employing asquare-wave oscillator operating a frequency on the order of l0,000Hertz, a high voltage AC output winding having means for avoidinginsulation burnout, comprising a core tube for supporting said windingthereon and adapted to receive a magnetic core therethrough, aconductive-material strip forming the inside first turn of said windingand having a beginning and an ending and being at least as wide as saidwinding,

said strip being wound around said core tube with said endingoverlapping said beginning,

electrical insulating means for separating said overlapping portions ofsaid strip,

the remainder of said winding being wound as multi turn layers incontinuation of said first turn and lying over said strip with the innerend thereof being electrically connected to said strip ending so thatsaid strip forms the first turn of said winding, and

means for making an electrical circuit connection to the beginning ofsaid strip.

11. The invention according to claim 10, wherein said means for makingan electrical circuit connection comprises a circuit connection to saidmagnetic core.

12. The invention according to claim 11, wherein said means for avoidinginsulation burn-out also comprises a second conductive-material stripforming at least the last turn of said winding and having a beginningand an ending and being at least as wide as said winding,

said second strip being wound around the outside of said winding withsaid beginning electrically connected to the outside end of saidwinding,

said second strip being more than one full turn of said winding andelectrical insulating means for separating said overlapping portions ofsaid second strip.

1. High-voltage AC inductive coil, comprising in combination a largeplurality of winding turns beginning at the inside of said coil andincluding multi-turn layers of an electrical conductor for developing ahigh-voltage output, the first turn of said winding turns comprising aunitary strip having a beginning and an ending and extending laterallysubstantially the entire width of said multiturn layers, said endingoverlapping said beginning and being insulated at said area of overlap,and means for connecting a lead conductor to said beginning of the firstturn.
 2. An inductive coil according to claim 1, further comprisingfirst electrically insulating sleeve means for supporting said windingsand being adapted to receive a magnetic core therein.
 3. An inductivecoil according to claim 2, further comprising second insulating meanslocated between each of said layers, and third insulating means forseparating each turn of said conductor from the others.
 4. An inductivecoil according to claim 3, further comprising electrically conductivemeans for connecting said lead conductor of said first turn to ground.5. An inductive coil according to claim 4, wherein said conductive meansis connected to said magnetic core.
 6. An inductive coil according toclaim 3, further comprising at least a last turn of said winding turnscomprising a unitary strip having a beginning and an ending andextending laterally substantially the entire width of said multiturnlayers, said ending overlapping said beginning and being insulated atsaid area of overlap, and means for connecting a lead conductor to theoutside end of said coil.
 7. An inductive coil according to claim 4,further comprising at least a last turn of said winding turns comprisinga unitary strip having a beginning and ending and extending laterallysubstantially the entire width of said multiturn layers, said endingoverlapping said beginning and being insulated at said area of overlap,and means for connecting a lead conductor to the outside end of saidcoil.
 8. An inductive coil according to claim 5, further comprising atleast a last turn of said winding turns comprising a unitary striphaving a beginning and and ending and extending laterally substantiallythe entire width of said multiturn layers, said ending overlapping saidbeginning and being insulated at said area of overlap, and means forconnecting a lead to the outside end of said coil.
 9. High-voltage ACinductive coil adapted for use in a secondary winding of a transformerfor use in an ignition system including a continuous square-wave-typeoscillator, comprising in combination a large plurality of winding turnsbeginning at the inside of said coil and including multiturn layers ofan electrical conductor for developing a high-voltage output, at leastthe first complete turn of said winding turns comprising a unitary striphaving a beginning and an ending and extending laterally substantiallythe entire width of said multiturn layers, said ending overlapping saidbeginning and being insulated at said area of overlap, means forconnecting a lead conductor to said beginning of the first turn, anelectrically insulating sleeve for having said windings wound thereonand adapted to receive a magnetic core therein, an insulating-materiallayer located between each of said winding layers, insulating means forseparating each of said turns from the others, at least a last completeturn of said winding turns comprising a unitary strip having a beginningand an ending and extending laterally substantially the entire width ofsaid multiturn layers and said ending overlapping said beginning andbeing insulated at said area of overlap, and means for connecting a leadto the outside end of said coil, an electrically conductive leadconnector for making an electrical connection between said beginning ofsaid first turn and ground, said ground including said magnetic core.10. In a transformer for use with an ignition system, employing asquare-wave oscillator operating a frequency on the order of 10,000Hertz, a high voltage AC output winding having means for avoidinginsulation burnout, comprising a core tube for supporting said windingthereon and adapted to receive a magnetic core therethrough, aconductive-material strip forming the inside first turn of said windingand having a beginning and an ending and being at least as wide as saidwinding, said strip being wound around said core tube with said endingoverlapping said beginning, electrical insulating means for separatingsaid overlapping portions of said strip, the remainder of said windingbeing wound as multiturn layers in continuation of said first turn andlying over said strip with the inner end thereof being electricallyconnected to said strip ending so that said strip forms the first turnof said winding, and means for making an electrical circuit connectionto the beginning of said strip.
 11. The invention according to claim 10,wherein said means for making an electrical circuit connection comprisesa circuit connection to said magnetic core.
 12. The invention accordingto claim 11, wherein said means for avoiding insulation burn-out alsocomprises a second conductive-material strip forming at least the lastturn of said winding and having a beginning and an ending and being atleast as wide as said winding, said second strip being wound around theoutside of said winding with said beginning electrically connected tothe outside end of said winding, said second strip being more than onefull turn of said winding and electrical insulating means for separatingsaid overlapping portions of said second strip.